The invention relates to a vane pump. In particular, the invention relates to a vane pump for use in a power steering system.
Usually, vane pumps with adjustable delivery volume, which are frequently also designated as adjustable pumps, are designed as follows: In essence, a cam ring or stroke contour ring and a rotatably movably mounted rotor are arranged in a pump housing. The rotor has radial slots, in which vanes are arranged such that they can be displaced radially and guided positively by the slots. During operation of the vane pump, the vanes thus slide along with their outer ends resting on the inner wall of the cam ring and, as a result, effect the delivery of a pressure medium (e.g. pressurized oil). As distinct from pumps with a constant delivery volume (constant delivery pumps), pumps with variable delivery volume are able to avoid the situation in which, in particular at high rotational speeds, overproduction of pressurized oil results, which, in the case of constant delivery pumps, must be partly compensated for by bypass circulation. Therefore, in constant delivery pumps in the higher rotational speed range, mechanically unusable energy is consumed by this bypass circulation, which is equivalent to an unnecessary loss of heat and energy. In order to control the delivery volume, in particular in order to reduce the delivery volume with increasing rotational speed, the eccentricity of the cam ring relative to the rotor is changed, in particular reduced. To this end, a conventional vane pump has a control device (e.g. control valve) with two outlets which, via control ducts, are able to supply a respective proportion of the delivered pressure medium to a left-hand and right-hand pressure chamber. The pressure chambers act from the left and the right on the outer surface of the cam ring and thus effect the desired change in the eccentricity of the cam ring relative to the rotor.
A vane pump of the type mentioned at the beginning is known, for example from the document DE 10 2004 060 082 A1 C1. By using FIGS. 1 to 3, the structure of such a conventional vane pump with adjustable delivery volume (adjustable pump for short) is illustrated.
FIGS. 1 and 3 show the structure of the known pump in cross section; FIG. 2 shows a three-dimensional illustration of the pump. The known adjustable pump VP has a pump housing G and a cam ring KR arranged therein (also called a stroke contour ring). A rotor R rotatably movably mounted therein is provided with a plurality of radial slots, in which vanes F are arranged such that they can be displaced radially and are positively guided and, during rotation, deliver a pressure medium DM from the suction side PSS to the pressure side PDS. To change the delivery volume, the position of the cam ring KR relative to the rotor R can be changed, so that the result is an adjustable eccentricity. For this purpose, the pump has two pressure chambers DK1 and DK2, which act from the left and right on the outer side of the cam ring KR, in which the pressure chambers are charged with a controllable proportion of the pressure medium DM. The control is achieved via a control device, which is usually designed as a control valve RV which has two outlets A1 and A2, in order to supply and discharge the proportion of the pressure medium via control ducts STK1 and STK2 to the pressure chambers in order that the different pressure in the chambers effects displacement of the cam ring KR relative to the rotor R, so that the desired eccentricity and therefore the desired geometric delivery volume is set.